The present invention pertains to the amplifier art and, more particularly, to an amplifying system having a quick responding automatic gain control.
Automatic gain control circuits are well known in the electronics art. Such circuits are commonly used in applications wherein a requirement is that an a.c. signal level be constrained within defined limits. For example, the communications art often requires that the dynamic range of audio information signals be compressed to minimize overloading of the transmitted signal while maintaining the average audio modulation at a high index and, thereby, increase the effective radiation area of the transmitter.
A substantial problem in many applications for audio gain control circuits is that conventional circuits do not have a quick response, or attack time. Attack time is that time necessary for the gain control circuit to attenuate a high level input signal to a desired level. This problem is particularly acute in single sideband transmitters wherein a slow attack time can result in clipping of the audio signal due to amplifier stage overloading. In fact, some circuits intentionally provide a clipper to prevent this overload condition. This clipping leads to loss of intelligibility of the transmitted information.